Project 1 comprises a component of our Hepatitis C virus Cooperative Research Center (HC CRC) U19 application. The focus of Project 1 is to understand the molecular mechanisms by which HCV is recognized by the host cell as a foreign pathogen to trigger immunity against infection, and to learn how HCV evades these processes to mediate infection outcome among clinical cases of HCV. HCV is a hepatotropic virus that mediates a persistent infection and chronic liver disease in millions of people worldwide. HCV persistence is associated with viral strategies to evade innate immune defenses and ap interferon (IFN) immune actions that normally limit Infection. We have identified HCV genome RNA and the cellular RIG-I protein as the viral pathogen-associated molecular pattern (PAMP) and host pathogen recognition receptor that Interact to trigger the expression of RIG-l-responsive genes that serve as immune effectors to control innate immunity and HCV infection. We have found that HCV can disrupt innate immune signaling via the actions of the viral NS3/4A protease, thus providing an evasion strategy that allows HCV to persist. We hypothesize that viral PAMP signaling and gene expression mediated through the RIG-I pathway are critical determinants controlling hepatic immunity and the outcome of HCV infection. Our studies are therefore deigned 1) Define the structure-function relationship of viral PAMP recognition by RIG-I among clinical isolates of HCV, 2) Identify the RIG-l-responsive genes of the liver that regulate HCV infection, and 3) Determine the function of NS3/4A to regulate the RIG-I pathway among clinical cases of HCV infected with different viral genotypes. Our studies are linked with the U19 Clinical Core, and Projects 2 and 3 to feature translational approaches aimed at defining the virus-host interface that controls hepatic innate immunity and HCV infection.